548 
ADRIAN J. PIETERS 
The fact that no examination was made before sixteen hours ex- 
plains why there is no apparent difference between the number of 
sporangia produced at 20° and at 28° C. It ma}^ also be noted how 
the higher temperature helps to conceal the difference in strength 
between the well- and the poorly-nourished mycelia. When many 
sporangia are formed at high temperatures it is really impossible for 
the observer to make a close comparison between them. At the low 
temperature, however, the difference in vigor is more clearly brought 
out. Here again, as noted before for Achlya racemosa, the difference 
between mycelia grown in 2 percent, 0.5 percent, and o.i percent 
peptone is not very marked though the first had food at a concentra- 
tion twenty times greater than the last. But as soon as the con- 
centration of the food falls below o.i percent the effect is quite marked ; 
the critical concentration lies between 0.1 and 0.05 percent. 
Production of oogo?iia. — It will be necessary before presenting the 
results of the experiments in which oogonia were counted to discuss 
more fully than was done earher the reliability of the method of 
counting the oogonia. When a mycelium is spread out between two 
glass plates the oogonia are sometimes scattered quite uniformly 
over the surface of the plate, but more often the largest number of 
oogonia lie near but not just at the margin and again near the thickest 
part of the mass, which is the original piece put into the dish of haemo- 
globin. When the oogonia are uniformly scattered the count can be 
made along any line, but sometimes the observer must select a line 
that will lie across an average field or must count along a second 
line at right angles to the first. It may be asked whether such a 
count will accurately represent the number of oogonia on a given 
mycelium. The answer to this is that with few exceptions two counts 
of oogonia on lines at right angles to each other agree closely. It may 
also be asked whether such a count means anything, whether it is 
not rather wholly fortuitous and whether another lot under the same 
conditions might not show a very different number. It must be ad- 
mitted that there is an element of uncertainty here which the writer 
would have been glad to eliminate. Living forms do not always 
behave with apparent uniformity; cases occurred in which the my- 
celium in one dish of a pair showed many oogonia while on the dupli- 
cate not one was to be found. Such instances however were excep- 
tional. As a rule the number of oogonia was nearly the same in each 
dish of a pair as will be seen from the tables and it is believed that 
